Process for treating high-sulfate organic wastewater

Abstract

The application provides a process method for treating high-sulfate organic wastewater, which comprises a pretreatment section, a concentration section and a salt separation section; the pretreatment section comprises a softening and adjusting unit, an electrodialysis I, ozone catalytic oxidation, two-stage biochemical treatment and a reuse water pool; the concentration section comprises a tubular microfiltration, a medium-high pressure reverse osmosis, a low-pressure reverse osmosis, an electrodialysis II and a biological reactor; wherein the electrodialysis adopts a modified anion exchange membrane, which is suitable for treating high-sulfate organic wastewater, effectively realizes the separation of salt and organic matters in the wastewater, has good anti-pollution capacity, and can realize the efficient removal of COD in the high-sulfate organic wastewater by combining with the freezing and crystallization technology; meanwhile, the salt is converted into high-purity sodium sulfate decahydrate and sodium chloride products, the wastewater is zero-emission, and the process has the advantages of mild operation condition, simple operation, low energy consumption and the like.

Description

TECHNICAL FIELD

[0001] The application relates to a treatment method of high-sulfate organic wastewater and belongs to the technical field of wastewater treatment. BACKGROUND

[0002] High-sulfate organic wastewater exists in various industries such as chemical industry, pharmaceutical industry, papermaking industry, food processing industry and mining industry. The wastewater has high salt concentration and is mainly composed of sulfate, and also has a certain concentration of organic matter (COD). If the organic matter content of conventional wastewater is high, the anaerobic method is usually used for treatment and methane is recovered. However, the high-sulfate organic wastewater contains a large amount of sulfate, and under anaerobic conditions, the sulfate is reduced to S 2- ions under the action of sulfate-reducing bacteria (SRB), the ions have strong biological toxicity and have a great inhibitory effect on microbial flora, and seriously affect the removal of organic matter. Therefore, the method generally requires that the sulfate concentration of the anaerobic reactor is less than 2000 mg / L, and the method is not applicable to high-sulfate wastewater, as disclosed in patent CN103771670A. Similarly, the high salt concentration also poses a problem for the use of the aerobic process, and the aerobic process also has aeration dead angle and local anaerobic bacteria, and when the sulfate concentration is too high, the sulfide concentration in the water body is also too high.

[0003] Under the background of increasingly strict wastewater discharge, the treatment of high-sulfate organic wastewater also faces a big problem, that is, the proper disposal of salt. At present, the salt separation technology mainly involves high-temperature evaporation crystallization, medium-temperature evaporation crystallization and cooling system, which has large energy consumption, and the material is easy to cause crystallization plugging of pipelines and equipment during the conversion between high and low temperatures. Meanwhile, the purity of the product is greatly affected by the temperature parameters and discharge parameters of each crystallizer, and the overall operation is difficult.

[0004] Membrane separation technology is a new technology that uses separation membranes as the core for separation, concentration and purification. Commonly used membrane separation technologies include ultrafiltration, nanofiltration and reverse osmosis. The membrane pore size of the above-mentioned membranes is in the nanometer level, which is very easy to be blocked by organic matter and suspended matter, and is mainly used for domestic water purification. In wastewater treatment, it is only limited to end desalination. Electrodialysis is a new technology formed on the basis of membrane separation combined with electrochemistry. The semi-permeable membrane used in electrodialysis is an ion exchange membrane, which realizes the separation of anions and cations under the driving of an external direct current electric field. Electrodialysis has been widely used in seawater desalination, brackish water desalination and the like due to its simple operation and long service life. However, for industrial wastewater, especially high-sulfate organic wastewater, the water contains not only soluble inorganic salt but also a large amount of organic matter and hardness, which will cause pollution and scaling of the ion exchange membrane in the separation and concentration process, thereby restricting the further development of the technology. SUMMARY

[0005] In view of the above deficiencies, the present application provides a process for treating high sulfate organic wastewater, which utilizes membrane technology, especially improved electrodialysis, and combines with freezing crystallization technology to achieve efficient removal of COD in high sulfate organic wastewater, while the salt is converted into high-purity sodium sulfate decahydrate and sodium chloride products, the wastewater is zero discharged, and the process has the advantages of mild operating conditions, simple operation and low energy consumption.

[0006] In order to achieve the above technical purposes, the technical solutions adopted by the present application are as follows:

[0007] The present application provides a process for treating high sulfate organic wastewater, wherein the mass concentration of sulfate in the high sulfate organic wastewater is greater than the mass concentration of chloride salt, the total salt mass concentration is greater than 8000 mg / L, and the COD is greater than 1000 mg / L.

[0008] The process comprises a pretreatment section, a concentration section and a salt separation section in sequence.

[0009] The pretreatment section comprises a softening adjustment unit, electrodialysis I, ozone catalytic oxidation, two-stage biochemical treatment and a reuse water tank; after softening adjustment, the wastewater enters electrodialysis I, the concentrated solution of electrodialysis I enters ozone catalytic oxidation, the dilution liquid enters two-stage biochemical treatment, and the effluent of two-stage biochemical treatment enters the reuse water tank; the effluent of ozone catalytic oxidation enters the tubular microfiltration of the concentration section.

[0010] The concentration section comprises tubular microfiltration, medium-high pressure reverse osmosis, low-pressure reverse osmosis, electrodialysis II and a biological reactor; the effluent of tubular microfiltration enters medium-high pressure reverse osmosis, the concentrated water of medium-high pressure reverse osmosis enters electrodialysis II, and the produced water enters low-pressure reverse osmosis; the concentrated solution of electrodialysis II enters the freezing crystallizer of the salt separation section, and the dilution liquid enters the biological reactor; the effluent of the biological reactor enters low-pressure reverse osmosis, the concentrated water of low-pressure reverse osmosis enters the ozone catalytic oxidation unit of the pretreatment section, and the produced water of low-pressure reverse osmosis enters the reuse water tank of the pretreatment section.

[0011] The salt separation section comprises a freezing crystallizer, nanofiltration and a salt crystallizer in sequence; the produced water of nanofiltration enters the salt crystallizer, and the concentrated water of nanofiltration and the mother liquor of the salt crystallizer are returned to the water inlet of electrodialysis II; the freezing crystallizer produces sodium sulfate decahydrate, and the salt crystallizer produces sodium chloride.

[0012] Further, the electrodialysis I and the electrodialysis II are composed of anion exchange membranes and cation exchange membranes, wherein the anion exchange membranes are modified anion exchange membranes, and the cation exchange membranes are general cation exchange membranes.

[0013] The modified anion exchange membrane is prepared by the following method:

[0014] Step a: linear high polymer is dissolved in organic solvent, then styrene, divinylbenzene, dioctyl phthalate, benzoyl peroxide and hydrophilic modifier are added respectively, the reaction is stirred to obtain a high polymer solution, wherein the hydrophilic modifier is selected from one or more of α-cyclodextrin, β-cyclodextrin or γ-cyclodextrin;

[0015] Step b: the high polymer solution prepared in step a is supplemented with organic solvent, anhydrous zinc chloride and chloromethyl methyl ether are added and stirred to react, then a precipitant is added, and after filtration, drying and crushing, a powdered chloromethylated polymer is obtained;

[0016] Step c: the polymer prepared in step b is dissolved in N,N-dimethylformamide, trimethylamine gas is introduced to perform quaternary amination reaction, and a quaternary aminated polymer solution is obtained; the quaternary aminated polymer solution is formed into a film; the obtained film is immersed in sodium hydroxide solution to perform alkalization, then washed with deionized water until neutral to obtain an anion exchange membrane;

[0017] Step d: polyanion modifier and sodium chloride are dissolved in Tris-HCl buffer solution, and the pH is adjusted to 8-9 with hydrochloric acid to obtain an electrodeposition mother liquor;

[0018] Step e: the anion exchange membrane obtained in step c is placed in the middle of a direct current electrodeposition device to form two compartments, the electrodeposition mother liquor prepared in step d is placed in the cathode side compartment, and water is placed in the anode side compartment, and an electrodeposition reaction is performed to obtain a modified anion exchange membrane.

[0019] Further, the linear high polymer in step a is at least one selected from polyethylene, polypropylene, polyvinyl chloride or polyvinylidene fluoride, and preferably polyvinyl chloride.

[0020] Further, the organic solvent in step a is one selected from dichloromethane, dichloroethane or chloroform, and preferably dichloromethane.

[0021] Further, the mass / volume concentration of the linear high polymer in the organic solvent in step a is 30-100 mg / mL, and the mass / volume concentrations of the styrene, divinylbenzene, dioctyl phthalate, benzoyl peroxide and hydrophilic modifier in the organic solvent are 20-100 mg / mL, 20-100 mg / mL, 5-20 mg / mL, 2-10 mg / mL and 30-50 mg / mL respectively.

[0022] Further, the stirring reaction in step a is performed at a temperature of 50-90°C for 0.5-6 h.

[0023] Further, the amount of the organic solvent supplemented in step b is 0.5-1 times the amount of the organic solvent used in step a.

[0024] Further, the mass-volume concentration of the anhydrous zinc chloride in the organic solvent in step b is 15-30 mg / mL, and the volume ratio of chloromethyl methyl ether to the organic solvent is 0.5:1-2:1.

[0025] Further, the temperature of the stirring reaction in step b is 30-55°C, and the time is 2-24 h.

[0026] Further, the precipitant in step b is methanol and / or ethanol.

[0027] Further, the mass-volume concentration of the polymer and N,N-dimethylformamide in step c is 15-40 mg / mL.

[0028] Further, the trimethylamine gas in step c is obtained by heating and vaporizing an aqueous trimethylamine solution and drying it with an alkaline drying agent. The alkaline drying agent is at least one selected from the group consisting of potassium hydroxide, sodium hydroxide, quicklime, and soda lime.

[0029] Further, the time of the quaternary amination reaction in step c is 10-120 minutes.

[0030] Further, the quaternary amination polymer solution in step c is cast or flow-casted to form a film, and then dried at a temperature of 50-70°C for 12-24 h.

[0031] Further, the concentration of the sodium hydroxide solution used for alkalization in step c is 0.1-1 mol / L.

[0032] Further, the concentration of the Tris-HCl buffer in step d is 10-50 mmol / L.

[0033] Further, the polyanion modifier in step d is one or more selected from the group consisting of poly(4-styrenesulfonic acid) sodium, p-styrenesulfonic acid sodium, polyvinylsulfonic acid sodium, and polypropylene sulfonic acid sodium, and is preferably poly(4-styrenesulfonic acid) sodium.

[0034] Further, the mass concentration of the polyanion modifier in the electrodeposition mother liquor in step d is 0.5-5 g / L, and the mass concentration of sodium chloride is 3-30 g / L.

[0035] Further, the electrodeposition reaction time in step e is 0.2-2 h, and the current density is 1-50 mA / cm 2 A layer of polyanion modifier is deposited on the surface of the anion exchange membrane by electrodeposition, which also sulfonates and modifies the membrane surface.

[0036] Further, the modified anion exchange membrane is stored in a sodium chloride solution after being obtained, and the mass concentration of the sodium chloride solution is 5-20 g / L.

[0037] The skilled in the art should understand that most of the polar organic pollutants existing in natural water or sewage, such as surfactants, humic acid, protein, etc. are negatively charged, and the anion exchange membrane is modified by the polyanion modifier, and the surface is negatively charged, which has electrostatic repulsion to the negatively charged organic matter in water, and can inhibit the organic pollution of the anion exchange membrane. The skilled in the art should also understand that the negative surface charge prevents the organic pollution by electrostatic effect, and also affects the migration rate of inorganic anions, and the more the ionic charge, the greater the influence, therefore, the sulfate ion is more affected than the chloride ion. The anion exchange membrane is added with a hydrophilic modifier during preparation, which can give the membrane strong hydrophilicity and change the migration rate of anions, and the migration number of anions with low hydration degree, such as bromide and nitrate, is reduced relative to that of chloride, and the migration number of sulfate ions with high hydration degree is increased relative to that of chloride. On the other hand, the hydrophilicity of the membrane is improved, the van der Waals force between the membrane and the organic solute is reduced, the attraction is reduced, and at the same time, the hydrophilic membrane and water molecules can form a hydration layer due to hydrogen bonding, which can further hinder the adsorption of pollutants on the membrane surface. Therefore, the anion exchange membrane of the present application is subjected to the combined action of the polyanion modifier and the hydrophilic modifier, the anti-pollution ability of the membrane is greatly increased, and the selective permeability of sulfate ions is increased.

[0038] Further, the softening of the softening adjustment unit is descaling, preferably a combined agent of sodium hydroxide and sodium carbonate, sodium hydroxide is added according to 1-4 times of the mass concentration of magnesium ions, and sodium carbonate is added according to 1-3 times of the mass concentration of calcium ions; the adjustment of the softening adjustment unit is pH adjustment, the acid used is sulfuric acid or hydrochloric acid, the base used is sodium hydroxide, and the pH adjustment range is 6-9.

[0039] Further, the treatment time of the electrodialysis I and the electrodialysis II is 0.5-3h, and the current density is 1-80mA / cm 2 .

[0040] Further, in the ozone catalytic oxidation, the ozone dosage is 0.1-2 times of the required oxidant dosage calculated according to the COD value of the wastewater, the reaction time is 10-120 minutes, and the catalyst is a conventional solid supported metal catalyst.

[0041] Further, the two-stage biochemical unit, i.e. the two-stage biological method is used to remove the organic matter in the dilution liquid of the electrodialysis I, since the electrodialysis I plays a role in separating organic matter and salt, the salt content in the dilution liquid is moderate, and conventional microorganisms can be used for removal; the two-stage biochemical unit is preferably a combination process of A / O process and BAF or A / O process and MBR.

[0042] Further, the tubular microfiltration is mainly used for filtering suspensions, colloids, microorganisms and the like to prevent the subsequent reverse osmosis membrane from being blocked.

[0043] Further, the medium-high pressure reverse osmosis unit is multi-stage and is composed of a plurality of medium-high pressure reverse osmosis membrane assemblies, the operating pressure is between 2.0 and 4.2 Mpa, the salt content of the wastewater can be concentrated to 40-110 g / L, and the overall concentration ratio is 2-10; the low pressure reverse osmosis is single-stage, the operating pressure is 1.0-2.0 Mpa, and the water production rate is 50%-80%.

[0044] Further, the biological reactor adopts the BAF or MBR process, and the biological bacteria strain adopts salt-tolerant bacteria. The salt-tolerant bacteria are salt-tolerant, especially sulfate-tolerant strains, and have strong tolerance to sulfides; preferably, the salt-tolerant bacteria GXNYJ-DL-1 disclosed in CN114686391A are used, and the preservation number is CGMCC No. 20350.

[0045] Further, the operating temperature of the freezing crystallizer is controlled to be 1-10 DEG C, the solubility of sodium sulfate is between 4.9 and 9.1 g / 100 g water at 1-10 DEG C, and the solubility of sodium chloride is greater than 35 g / 100 g water, so that sodium sulfate decahydrate can be precipitated by cooling at this temperature, and sodium chloride is in a dissolved state; the purity of sodium sulfate decahydrate product of the freezing crystallizer is greater than 99%; further, the sodium sulfate decahydrate can be further dehydrated to obtain sodium sulfate.

[0046] Further, the nanofiltration has good selective permeability to chloride ions and good interception effect on sulfate ions, the interception rate of sulfate ions is greater than 90%, and the nanofiltration water production rate is 60%-85%.

[0047] Further, the operating temperature of the salt crystallizer is controlled to be 35-60 DEG C, and concentrated mother liquor is obtained in addition to the sodium chloride product; further, when the salt crystallizer works for a period of time, the sodium sulfate concentration of the concentrated mother liquor is as high as 300 g / L, and the concentrated mother liquor is returned to the second treatment of the electrodialysis II, according to the solubility of sodium sulfate between (40 g-49 g) / 100 g water at 35-60 DEG C, when the sodium sulfate concentration is lower than 300 g / L, the sodium sulfate in the salt crystallizer can be ensured to be in a dissolved state at all times, and the purity of the precipitated sodium chloride product is not affected.

[0048] Compared with the prior art, the present application has the following advantages:

[0049] (1) In the pretreatment section, the modified anion exchange membrane and improved electrodialysis of the present application can effectively realize the separation of salt and organic matter in high sulfate organic wastewater, solve the problem of difficult treatment of organic matter in high sulfate organic wastewater, and the modified anion exchange membrane has the characteristics of strong anti-pollution ability and high ion exchange rate, and has high application value.

[0050] (2) In the concentration section, the modified anion exchange membrane and improved electrodialysis of the present application not only realizes the concentration of salt, but also retains most of the organic matter in the dilution liquid, thereby reducing the organic matter content in the salt separation section and greatly increasing the product purity.

[0051] (3) In the salt separation section, the sodium sulfate prepared by the freezing crystallization method is converted from liquid phase to solid phase by cooling under the condition that the wastewater is not obviously concentrated, and at this time, sodium chloride is in a completely dissolved state in liquid phase, so that high-purity sodium sulfate decahydrate can be obtained; after the sodium sulfate is separated by freezing crystallization, the concentration of sodium sulfate in the effluent is much lower than that of sodium chloride, and the sodium sulfate is further removed by the nanofiltration unit, so that the proportion of sodium chloride in the solution is very high, which is more conducive to the salt crystallizer to obtain sodium chloride with higher purity.

[0052] (4) The freezing crystallization method for preparing sodium sulfate has a heat exchange temperature difference of only 25-30℃, which has a significant energy consumption advantage compared with the traditional heat method with a heat exchange temperature difference of 70-100℃. Moreover, the separation of salt and organic matter, the separation of sodium sulfate and sodium chloride, and the crystallization of sodium sulfate and sodium chloride are all carried out under normal temperature or low temperature conditions by means of improved electrodialysis, reverse osmosis, nanofiltration and other membrane technologies, so that the high-sulfate organic wastewater is truly treated by the full "cold method", the overall operation condition is mild, the operation is simple and easy to control, and the cost advantage is obvious.

[0053] Other features and advantages of the present application will be described in detail in the following specific embodiments. BRIEF DESCRIPTION OF DRAWINGS

[0054] Figure 1 The process flow diagram of the treatment of high sulfate organic wastewater in Example 1 is shown in

[0055] Figure 2 The schematic diagram of the anion exchange membrane electrodeposition modification in Example 1 is shown in DETAILED DESCRIPTION

[0056] The present application will be further described in detail below in conjunction with specific embodiments. The embodiments are implemented on the premise of the technical solutions of the present application, and detailed implementation modes and specific operation processes are given, but the protection scope of the present application is not limited to the following embodiments.

[0057] Example 1

[0058] The process flow diagram of the treatment of high sulfate organic wastewater is shown in Figure 1As shown, the high sulfate organic wastewater first enters the softening adjusting tank, and after hardening and pH adjustment, enters the electrodialysis I; the dilute liquid of the electrodialysis I is treated by two-stage biochemical units and then discharged to the reuse water tank, and the concentrated liquid of the electrodialysis I enters the ozone catalytic oxidation; the effluent of the ozone catalytic oxidation is filtered by the tubular microfiltration and then enters the medium-high pressure reverse osmosis, and the produced water of the medium-high pressure reverse osmosis is treated by the low pressure reverse osmosis and then discharged to the reuse water tank, and the concentrated water is returned to the ozone catalytic oxidation for secondary treatment; the concentrated water of the medium-high pressure reverse osmosis flows to the electrodialysis II, the dilute liquid of the electrodialysis II flows to the biological reactor, the salt-tolerant bacteria are added to the biological reactor, and the effluent enters the low pressure reverse osmosis; the concentrated liquid of the electrodialysis II enters the refrigeration crystallizer to obtain the product sodium sulfate decahydrate, and the remaining mother liquor enters the nanofiltration unit, the produced water of the nanofiltration enters the salt crystallizer to obtain the product sodium chloride, and the nanofiltration concentrated water and the concentrated mother liquor of the salt crystallizer are returned to the electrodialysis II for secondary treatment.

[0059] The process method of the application is used for treating high sulfate organic wastewater.

[0060] A high sulfate organic wastewater, whose water quality is as follows: COD 1200mg / L, sulfate 4000mg / L, chloride salt concentration 3000mg / L, belongs to a typical high sulfate organic wastewater. In addition, the calcium ion concentration is 150mg / L, the magnesium ion concentration is 50mg / L, the total salt content is 11000mg / L, the pH is 5, the wastewater flow is 20t / h, the mass concentration ratio of sulfate to chloride salt is 4:3, and the organic matter in the wastewater is mainly neutral organic matter (uncharged).

[0061] The electrodialysis I and the electrodialysis II provided in the embodiment are both modified electrodialysis, wherein the anion exchange membrane is a modified anion exchange membrane, the anti-pollution ability is strong, the ion permeation rate is high, and the cation exchange membrane is a general cation exchange membrane (CJ-MC-3, China Hefei Kaitie Polymer Co., Ltd.).

[0062] The modified anion exchange membrane is prepared by the following method:

[0063] In step a, the linear high polymer is dissolved in 1 volume unit of an organic solvent, the mass volume concentration of the linear high polymer and the organic solvent is 65mg / mL, and styrene, divinylbenzene, dioctyl phthalate, benzoyl peroxide and a hydrophilic modifier are added in mass volume concentrations of 45mg / mL, 40mg / mL, 9mg / mL, 6mg / mL and 40mg / mL respectively, and stirring reaction is carried out at a temperature of 70℃ for 2.5h to obtain a high molecular polymer solution; the linear high polymer is polyvinyl chloride, the organic solvent is dichloromethane, and the hydrophilic modifier is β-cyclodextrin.

[0064] Step b, supplement 0.6 volume units of organic solvent to the high molecular polymer solution prepared in step a, add anhydrous zinc chloride and chloromethyl methyl ether, the mass volume concentration of anhydrous zinc chloride and solvent is 22 mg / mL, the volume ratio of chloromethyl methyl ether and solvent is 1.3:1, after stirring at 45℃ for 10h, add precipitant methanol, filter, dry, crush, to obtain powder chloromethylated polymer;

[0065] Step c, dissolve the polymer prepared in step b in N,N-dimethylformamide, the mass volume concentration of polymer and N,N-dimethylformamide is 26 mg / mL; heat and vaporize the aqueous trimethylamine solution, pass the trimethylamine gas through the basic drying agent after drying, and then pass it into the N,N-dimethylformamide solution of the above polymer, the reaction time is 60 minutes, to obtain a quaternary aminated polymer solution; use casting method to prepare a film from the quaternary aminated polymer solution, and dry at 65℃ for 15h to form a film; immerse the obtained film in 0.5 mol / L sodium hydroxide solution for alkalization, and then wash with deionized water until neutral to obtain an anion exchange membrane;

[0066] Step d, dissolve the polyanion modifier and sodium chloride in 20 mmol / L Tris-HCl buffer, adjust the pH to 8.5 with hydrochloric acid, the mass concentration of polyanion modifier is 3 g / L, and the mass concentration of sodium chloride is 10 g / L, to prepare an electrodeposition mother liquor; the polyanion modifier is selected from poly 4-styrene sulfonic acid sodium;

[0067] Step e, take the anion exchange membrane prepared in step c, and modify and decorate the surface by electrodeposition method, as shown in Figure 2 , that is, place the preliminarily modified anion exchange membrane in the middle of a direct current electrodeposition device to form two compartments, put the electrodeposition mother liquor prepared in step d in the cathode side compartment, and put water in the anode side compartment, the electrodeposition time is 0.8h, and the current density is 20mA / cm 2 , to obtain the modified anion exchange membrane;

[0068] Step f: take out the modified anion exchange membrane prepared in step e and place it in a sodium chloride solution with a mass concentration of 10 g / L for use.

[0069] The specific operation parameters for treating high sulfate organic wastewater are as follows:

[0070] The wastewater first enters the softening adjustment tank, and the hardening agent is added according to the mass concentration of sodium hydroxide 120 mg / L and the mass concentration of sodium carbonate 280 mg / L, and the pH is adjusted to 7 with sodium hydroxide, and after clarification, the calcium ion concentration of the supernatant is reduced to below 10 mg / L, and the magnesium ion concentration is reduced to below 5 mg / L, and the effluent enters the electrodialysis I; the treatment time of electrodialysis I is 1h, and the current density is 25mA / cm 2, the COD concentration of the dilute liquid in the electrodialysis I after treatment is 1558 mg / L, the salt content is 2535 mg / L, the flow rate is 15 t / h, the COD concentration of the concentrated liquid is 126 mg / L, the salt content is 36395 mg / L, the flow rate is 5 t / h, the selective permeation rate of sulfate ions is 78.5%, the selective permeation rate of chloride ions is 85.8%, and the interception rate of organic matter is 97.3%; the dilute liquid in the electrodialysis I enters two-stage biochemical units, the A / O process is used in the first-stage biochemical process, the MBR process is used in the second-stage biochemical process, because the salt content is low, the conventional activated sludge is added, the residence time of the A / O process is 36 h, the residence time of the MBR process is 12 h, the COD concentration of the final effluent is 46 mg / L, the salt content is 2510 mg / L, which meets the recycling standard and enters the recycling pool; the electrodialysis concentrated liquid enters the ozone catalytic oxidation unit, the ozone addition concentration is 100 mg / L, the reaction time is 30 min, the effluent COD is 66 mg / L, and the effluent is filtered through the tubular microfiltration and then enters the medium-high pressure reverse osmosis unit.

[0071] The operation pressure of the medium-high pressure reverse osmosis is between 3 and 4.2 Mpa, the salt content of the concentrated water after concentration is close to 100 g / L, and the concentration multiple is 2.7; the salt content of the medium-high pressure reverse osmosis produced water is 3-10 g / L, which enters the low pressure reverse osmosis, the low pressure reverse osmosis is one-stage, the operation pressure is 1.5 Mpa, the water production rate is 70%, the salt content of the concentrated water is greater than 10 g / L, and the COD is higher than 60 mg / L, which is returned to the ozone catalytic oxidation unit for secondary treatment, the COD of the low pressure reverse osmosis produced water is lower than 60 mg / L, the salt content is lower than 2500 mg / L, which meets the recycling requirement; the medium-high pressure reverse osmosis concentrated water enters the electrodialysis II, the salt content of the medium-high pressure reverse osmosis concentrated water is about 100 g / L, the COD is 175 mg / L, the treatment time of the electrodialysis II is 1.2 h, the current density is 25 mA / cm 2 , the salt content of the electrodialysis II concentrated liquid after treatment is about 200 g / L, the COD is 35 mg / L, the water amount of the concentrated liquid accounts for 40% of the total water amount, the salt content of the dilute liquid is about 33 g / L, the COD is 268 mg / L, and the water amount of the dilute liquid accounts for 60% of the total water amount; the electrodialysis II dilute liquid enters the biological reactor, the BAF process is used, the salt-tolerant bacteria are added, the salt-tolerant bacteria GXNYJ-DL-1 disclosed in the patent CN114686391A is selected, the preservation number is CGMCC No.20350, the residence time is 6 h, the effluent COD is as low as 80 mg / L, the COD is less than 40 mg / L after the low pressure reverse osmosis treatment, and the salt content is lower than 2500 mg / L, which meets the recycling requirement.

[0072] The concentrated solution from electrodialysis II enters the cryo-crystallizer, where the temperature is controlled at 4°C. Sodium sulfate decahydrate precipitates due to its reduced solubility, resulting in a product purity of 99.2%. The remaining mother liquor contains approximately 160 g / L of sodium chloride, which is in a dissolved state, and approximately 50 g / L of sodium sulfate. The effluent from the cryo-crystallizer enters the nanofiltration unit, producing 60% nanofiltration permeate. The nanofiltration permeate has a sodium sulfate concentration of approximately 2 g / L, a sodium chloride concentration of approximately 200 g / L, and a COD of approximately 100 mg / L. This permeate then enters the salt crystallizer, where the concentrated nanofiltration solution has a sodium sulfate concentration of approximately 122 g / L, a sodium chloride concentration of approximately 100 g / L, and a COD of approximately 200 mg / L. This concentrated nanofiltration solution is returned to electrodialysis II for secondary treatment. The salt crystallizer is controlled at 45°C, and crystallization yields sodium chloride with a purity of 99.6%. When the mother liquor is concentrated to a sodium sulfate concentration of 300 g / L, to avoid affecting product purity, the concentrated mother liquor is returned to electrodialysis II for secondary treatment.

[0073] As demonstrated in this embodiment, the present invention can effectively treat high-sulfate organic wastewater. Through improved electrodialysis separation pretreatment, most of the wastewater is recycled after simple biochemical treatment. High-salt components are moderately treated by ozone catalytic oxidation, and then concentrated and separated using membrane technologies such as reverse osmosis, improved electrodialysis, and nanofiltration, ultimately achieving zero discharge and producing high-purity sodium chloride and sodium sulfate decahydrate. The overall process route operates under mild conditions, is simple to operate, and has low energy consumption.

[0074] Example 2

[0075] use Figure 1 The process shown is for treating a wastewater with high sulfate and high organic content.

[0076] The wastewater quality is as follows: COD 1500 mg / L, sulfate 6000 mg / L, chloride concentration 3000 mg / L, classifying it as high sulfate and high organic wastewater. Additionally, the calcium ion concentration is 100 mg / L, the magnesium ion concentration is 100 mg / L, the total salt content is 14000 mg / L, the pH is 10, the wastewater flow rate is 20 t / h, the sulfate to chloride mass ratio is 2:1, and the organic matter in the wastewater is mainly neutral organic matter (uncharged).

[0077] The process route and implementation steps for treating high-sulfate organic wastewater in this embodiment are the same as in Example 1. Electrodialysis I and Electrodialysis II in the process route are the same as in Example 1, both being modified electrodialysis methods. The anion exchange membrane is a modified anion exchange membrane, and the cation exchange membrane is a general-purpose cation exchange membrane (Hefei Kaijie Polymer Co., Ltd., China, model CJ-MC-3). In the preparation of the modified anion exchange membrane, except that the linear polymer in step a is polyethylene, the β-cyclodextrin mass-volume concentration is 50 mg / mL, the volume ratio of chloromethyl ether to solvent in step b is 1.4:1, and the stirring reaction time is 12 h, everything else is the same as in Example 1.

[0078] The specific operating parameters for treating the high sulfate high organic wastewater are as follows:

[0079] The wastewater first enters a softening adjusting tank, and a descaling agent is added according to a sodium hydroxide mass concentration of 200 mg / L and a sodium carbonate mass concentration of 200 mg / L, and sulfuric acid is added to adjust the pH to 7.5. After clarification, the supernatant calcium ion concentration is reduced to below 8 mg / L, and the magnesium ion concentration is reduced to below 6 mg / L. The effluent enters the electrodialysis I; the treatment time of the electrodialysis I is 1.1 h, and the current density is 28 mA / cm 2 After treatment, the dilute liquid in the electrodialysis I has a COD concentration of 2052 mg / L, a salt content of 2925 mg / L, a flow rate of 14 t / h, a concentrated liquid COD concentration of 210 mg / L, a salt content of 39841 mg / L, a flow rate of 6 t / h, a sulfate ion selective permeation rate of 81.5%, a chloride ion selective permeation rate of 87.8%, and an organic matter interception rate of 95.7%; the dilute liquid of the electrodialysis I enters a two-stage biochemical unit, a primary biochemical process adopts an A / O process, and a secondary biochemical process adopts a BAF process. Since the salt content is moderate, conventional activated sludge is added, the A / O process has a residence time of 40 h, the BAF process has a residence time of 15 h, the final effluent has a COD concentration of 56 mg / L and a salt content of 2945 mg / L, which meets the reuse standard and enters a reuse tank; the electrodialysis concentrated liquid enters an ozone catalytic oxidation unit, the ozone addition concentration is 120 mg / L, the reaction time is 30 min, the effluent COD is 115 mg / L, and the effluent is filtered by a tubular microfiltration and then enters a medium-high pressure reverse osmosis unit.

[0080] The medium-high pressure reverse osmosis operating pressure is between 3 and 4.2 Mpa. After concentration, the concentrated water salt content is close to 90 g / L, and the concentration ratio is 2.3. The medium-high pressure reverse osmosis produced water salt content is 3-12 g / L, which enters a low pressure reverse osmosis. The low pressure reverse osmosis is a primary process, the operating pressure is 1.5 Mpa, the water production rate is 68%, the concentrated water salt content is greater than 10 g / L, and the COD is higher than 60 mg / L, which is returned to the ozone catalytic oxidation unit for secondary treatment. The low pressure reverse osmosis produced water COD is lower than 60 mg / L, the salt content is lower than 2500 mg / L, which meets the reuse requirements. The medium-high pressure reverse osmosis concentrated water enters the electrodialysis II. The medium-high pressure reverse osmosis concentrated water salt content is about 90 g / L, and the COD is 250 mg / L. The electrodialysis II treatment time is 1.2 h, and the current density is 28 mA / cm 2, the salt content of the concentrated solution of the electro-dialysis II is about 190 g / L, the COD is 45 mg / L, the water volume of the concentrated solution accounts for 38% of the total water volume of the influent, the salt content of the diluted solution is about 29 g / L, the COD is 375 mg / L, and the water volume of the diluted solution accounts for 62% of the total water volume of the influent; the diluted solution of the electro-dialysis II enters a biological reactor, an MBR process is adopted, salt-tolerant bacteria are added, the salt-tolerant bacteria GXNYJ-DL-1 disclosed in the patent CN114686391A are selected, the preservation number is CGMCC No. 20350, the residence time is 9 h, the effluent COD is as low as 80 mg / L, the effluent is treated by low-pressure reverse osmosis again, the COD is less than 40 mg / L, the salt content is less than 2500 mg / L at the same time, and the requirements for recycling are met.

[0081] The concentrated solution of the electro-dialysis II enters a freezing crystallizer, the temperature is controlled at 5℃, sodium sulfate decahydrate is precipitated due to the reduction of solubility, the product purity is 99.3%, the sodium chloride concentration in the remaining mother liquor is about 155 g / L and is in a dissolved state, and the sodium sulfate concentration in the remaining mother liquor is about 52 g / L; the effluent of the freezing crystallizer enters a nanofiltration unit, the nanofiltration water yield is 65%, the sodium sulfate concentration in the nanofiltration water is about 3 g / L, the sodium chloride concentration is about 190 g / L, and the COD is about 135 mg / L; the nanofiltration water enters a salt crystallizer, the sodium sulfate concentration in the nanofiltration concentrated water is about 143 g / L, the sodium chloride concentration is about 90 g / L, and the COD is about 260 mg / L; the nanofiltration concentrated water returns to the electro-dialysis II for secondary treatment; the salt crystallizer is controlled at a temperature of 48℃, and sodium chloride with a purity of 99.5% is obtained by crystallization; when the mother liquor is concentrated to a sodium sulfate mass concentration of 300 g / L, the concentrated mother liquor returns to the electro-dialysis II for secondary treatment without affecting the product purity.

[0082] It can be seen from the embodiment that the application can effectively treat high-sulfate organic wastewater with different concentrations, the wastewater finally achieves zero discharge, and high-purity sodium chloride and sodium sulfate decahydrate are prepared. The overall process route has mild operating conditions, simple operation, and low energy consumption.

[0083] Comparative Example 1

[0084] The wastewater treated in Comparative Example 1 has the same water quality as that in Example 2, the process route and implementation steps are also the same as those in Example 2, and the difference is that the anion exchange membrane and the cation exchange membrane of the electro-dialysis I are both general type membranes and are not modified, the anion exchange membrane is a product of Asahi Glass Company, Japan (SELEMION AMV), and the cation exchange membrane is a product of Hefei Kaitai Polymer Co., Ltd., China (model CJ-MC-3).

[0085] Specifically, the wastewater first enters a softening adjustment tank, the adding amount of sodium hydroxide and sodium carbonate is the same as that in Example 2, and the effluent enters the ordinary electro-dialysis I; the treatment time of the ordinary electro-dialysis I is 1.1 h, the current density is 28 mA / cm 2, the desalination liquid COD concentration in the post-treatment electrodialysis was 1732 mg / L, the salt content was 5511 mg / L, the flow rate was 14 t / h, the concentrated liquid COD concentration was 957 mg / L, the salt content was 33807 mg / L, the flow rate was 6 t / h, the sulfate ion selective permeability was 68.5%, and the chloride ion selective permeability was 75.4%, which was obviously decreased compared with Example 2, and the membrane flux was obviously decreased, which might be related to membrane clogging. In addition, the organic matter retention rate was reduced to 80.8%, indicating that a large amount of negatively charged organic matter passed through the anion membrane, increasing the possibility of membrane clogging; the desalination liquid after the first-stage electrodialysis I treatment entered a two-stage biochemical unit, the first-stage biochemical treatment adopted A / O process, the second-stage biochemical treatment adopted BAF process, and conventional activated sludge was added, the A / O process residence time was 40 h, the BAF process residence time was 15 h, the final effluent COD concentration was 565 mg / L, and the salt content was 5425 mg / L, which did not reach the reuse standard, and the analysis showed that the high salt concentration led to poor biochemical effect; at the same time, the concentrated liquid of the electrodialysis I entered an ozone catalytic oxidation unit, the ozone addition concentration was 120 mg / L, the reaction time was 30 min, the effluent COD was 795 mg / L, and the effluent was filtered through a tubular microfiltration and then entered a medium-high pressure reverse osmosis unit, and due to the high COD concentration, the reverse osmosis unit was seriously clogged.

[0086] From the present comparative example, it can be seen that the electrodialysis I adopts unmodified cation and anion exchange membranes, which cannot effectively separate organic matter and salt, thereby leading to high salt content in the biochemical unit, and the wastewater cannot be treated to reach the reuse standard, and the organic matter concentration in the concentration unit is too high, and the salt concentration section and the salt separation section cannot normally operate.

[0087] Comparative Example 2

[0088] Comparative Example 2

[0089] Specifically, the wastewater was pretreated and concentrated, and then the high-pressure reverse osmosis unit concentrated water entered the electrodialysis II, the medium-high pressure reverse osmosis concentrated water salt content was about 90 g / L, and the COD was 250 mg / L; the electrodialysis II treatment time was 1.2 h, the current density was 28 mA / cm 2, the salt content of the concentrated solution of the electro-dialysis II is about 163 g / L, the COD is 150 mg / L, the water volume of the concentrated solution accounts for 38% of the total water volume of the inlet water, the salt content of the diluting solution is about 45 g / L, the COD is 311 mg / L, and the water volume of the diluting solution accounts for 62% of the total water volume of the inlet water; the diluting solution of the electro-dialysis II enters the biological reactor, the MBR process is adopted, the salt-tolerant bacteria are added, the salt-tolerant bacteria GXNYJ-DL-1 disclosed in the patent CN114686391A is selected, the preservation number is CGMCC No. 20350, the residence time is 9 h, the COD of the effluent water is as low as 70 mg / L, and the effluent water enters the low-pressure reverse osmosis; the water production rate of the low-pressure reverse osmosis is 68%, the COD of the effluent water of the low-pressure reverse osmosis is less than 40 mg / L, and the salt content is 3670 mg / L; the general industrial water such as circulating water requires that the salt content is less than 3000 mg / L, and therefore the effluent water of the reverse osmosis cannot meet the recycling requirements; the salt content of the concentrated solution of the electro-dialysis II is relatively low, the COD is relatively high, and finally the crystallization efficiency of the subsequent process is reduced, the purity of the sodium sulfate decahydrate is reduced to 98.4%, and the purity of the sodium chloride is reduced to 98.6%.

[0090] It can be known from the present comparative example that the electro-dialysis II adopts the unmodified cation and anion exchange membranes, the separation ability of the cation and anion exchange membranes for organic matters and salt is poor, and the anion exchange membrane is easily polluted by the organic matters, so that the diluting solution is difficult to be treated to meet the recycling requirements, and the purity of the sodium sulfate decahydrate and the sodium chloride prepared from the concentrated solution is reduced.

Claims

1. A process for treating high-sulfate organic wastewater, wherein the mass concentration of sulfate is greater than that of chloride, the total salt mass concentration is greater than 8000 mg / L, and the COD is greater than 1000 mg / L; the process comprises, in sequence, a pretreatment section, a concentration section, and a salt separation section; the pretreatment section comprises a softening and adjusting unit, an electrodialysis I, ozone catalytic oxidation, two-stage biochemical treatment, and a reuse water tank; wastewater is fed into the electrodialysis I after softening and adjusting, the concentrated solution of the electrodialysis I is fed into the ozone catalytic oxidation, the dilution liquid is fed into the two-stage biochemical treatment, and the effluent of the two-stage biochemical treatment is fed into the reuse water tank; the effluent of the ozone catalytic oxidation is fed into the tubular microfiltration of the concentration section; the concentration section comprises the tubular microfiltration, medium-high pressure reverse osmosis, low pressure reverse osmosis, electrodialysis II, and a biological reactor; the effluent of the tubular microfiltration is fed into the medium-high pressure reverse osmosis, the concentrated water of the medium-high pressure reverse osmosis is fed into the electrodialysis II, and the produced water is fed into the low pressure reverse osmosis; the concentrated solution of the electrodialysis II is fed into the freeze crystallizer of the salt separation section, and the dilution liquid is fed into the biological reactor; the effluent of the biological reactor is fed into the low pressure reverse osmosis, the concentrated water of the low pressure reverse osmosis is fed into the ozone catalytic oxidation of the pretreatment section, and the produced water of the low pressure reverse osmosis is fed into the reuse water tank of the pretreatment section; the salt separation section comprises, in sequence, the freeze crystallizer, nanofiltration, and a salt crystallizer; the produced water of the nanofiltration is fed into the salt crystallizer, and the concentrated water of the nanofiltration and the mother liquor of the salt crystallizer are fed together back to the water inlet of the electrodialysis II; the freeze crystallizer produces sodium sulfate decahydrate as a product, and the salt crystallizer produces sodium chloride as a product; the electrodialysis I and the electrodialysis II are composed of anion exchange membranes and cation exchange membranes, wherein the anion exchange membranes are modified anion exchange membranes, and the cation exchange membranes are general cation exchange membranes; the modified anion exchange membranes are prepared by the following method: step a: linear high polymer is dissolved in an organic solvent, then styrene, divinylbenzene, dioctyl phthalate, benzoyl peroxide, and a hydrophilic modifier are added respectively, and the mixture is stirred and reacted to obtain a high polymer solution, wherein the hydrophilic modifier is selected from one or more of α-cyclodextrin, β-cyclodextrin, and γ-cyclodextrin; step b: the high polymer solution prepared in step a is supplemented with organic solvent, anhydrous zinc chloride, and chloromethyl methyl ether are added, and the mixture is stirred and reacted, then a precipitant is added, and after filtration, drying, and crushing, a chloromethylated polymer powder is obtained; step c: the chloromethylated polymer prepared in step b is dissolved in N, N-dimethylformamide, and trimethylamine gas is introduced to perform quaternary amination, thereby obtaining a quaternary aminated polymer solution; the quaternary aminated polymer solution is formed into a membrane; the obtained membrane is immersed in a sodium hydroxide solution to perform alkalization, then washed with deionized water until neutral, and an anion exchange membrane is obtained; step d: a polyanion modifier is dissolved in a Tris-HCl buffer solution, and the pH is adjusted to 8-9 with hydrochloric acid to obtain an electrodeposition mother liquor; the polyanion modifier is selected from one or more of poly (4-sodium styrene sulfonate), p-sodium styrene sulfonate, poly (sodium ethylene sulfonate), and poly (sodium propylene sulfonate). ​ ​ ​ ​ wherein ​ ​ ​ ​ ​ ​ Step e: the anion exchange membrane obtained in step c is placed in the middle of a direct current electrodeposition device to form two compartments, the cathode side compartment is put into the electrodeposition mother liquor prepared in step d, and the anode side compartment is put into water to carry out electrodeposition reaction to obtain a modified anion exchange membrane.

2. The process of claim 1, wherein, The linear polymer in step a is at least one of polyethylene, polypropylene, polyvinyl chloride or polyvinylidene fluoride; the organic solvent is one of dichloromethane, dichloroethane or chloroform; the mass-volume concentration of the linear polymer in the organic solvent is 30-100 mg / mL.

3. The process of claim 1, wherein, The mass-volume concentration of the styrene, divinylbenzene, dioctyl phthalate, benzoyl peroxide and hydrophilic modifier in the organic solvent in step a is 20-100 mg / mL, 20-100 mg / mL, 5-20 mg / mL, 2-10 mg / mL and 30-50 mg / mL, respectively.

4. The process of claim 1, wherein, The stirring reaction temperature in step a is 50-90°C, and the time is 0.5-6 h.

5. The process of claim 1, wherein, The additional amount of the organic solvent in step b is 0.5-1 times of the amount used in step a; the mass-volume concentration of the anhydrous zinc chloride in the organic solvent in step b is 15-30 mg / mL, and the volume ratio of chloromethyl methyl ether to the organic solvent is 0.5:1-2:

1.

6. The process of claim 1, wherein, The stirring reaction temperature in step b is 30-55°C, and the time is 2-24 h.

7. The process of claim 1, wherein, The mass-volume concentration of the chloromethylated polymer and N,N-dimethylformamide in step c is 15-40 mg / mL; the trimethylamine gas is obtained by heating and vaporizing an aqueous trimethylamine solution and drying it with a basic drying agent.

8. The process of claim 1, wherein, The time of the quaternary amination reaction in step c is 10-120 minutes; the quaternary aminated polymer solution is cast or flow-casted to form a film, and then dried at a temperature of 50-70°C for 12-24 h.

9. The process of claim 1, wherein, The mass concentration of the polyanion modifier in the electrodeposition mother liquor in step d is 0.5-5 g / L, and the mass concentration of sodium chloride is 3-30 g / L.

10. The process of claim 1, wherein, The electrodeposition reaction time of step e is 0.2-2 h and the current density is 1-50 mA / cm 2 .

11. The process of claim 1, wherein, The softening of the softening adjustment unit is hardening removal, and a combined agent of sodium hydroxide and sodium carbonate is used, sodium hydroxide is added according to 1-4 times of the mass concentration of magnesium ions, and sodium carbonate is added according to 1-3 times of the mass concentration of calcium ions, and the pH is adjusted to 6-9 with acid or base.

12. The process of claim 1, wherein, The treatment time of the electrodialysis I and the electrodialysis II is 0.5-3h respectively, and the current density is 1-80mA / cm 2 .

13. The process of claim 1, wherein, In the ozone catalytic oxidation, the ozone dosage is 0.1-2 times of the required oxidant dosage calculated according to the COD value of the wastewater, and the reaction time is 10-120 minutes.

14. The process of claim 1, wherein, The two-stage biochemical process is the combination of A / O process and BAF or A / O process and MBR.

15. The process of claim 1, wherein, The operating pressure of the medium-high pressure reverse osmosis is between 2.0-4.2 Mpa, and the salt concentration of the wastewater is concentrated to 40-110 g / L; the low-pressure reverse osmosis is a single stage, the operating pressure is 1.0-2.0 Mpa, and the water production rate is 50%-80%.

16. The process of claim 1, wherein, The operating temperature of the freezing crystallizer is controlled at 1-10°C.

17. The process of claim 1, wherein, The operating temperature of the salt crystallizer is controlled at 35-60°C to obtain sodium chloride product and concentrated mother liquor.

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